The present invention relates generally to a power down system and method for power changes in a power distribution network, and relates more particularly to a programmable power down policy to be applied during a power change in a power distribution network.
The development of sophisticated networks for transferring information has driven a number of technologies including the provision of power over network connections. For example, a network connected device for transferring information over the network may receive power from the network so that alternate power sources for the device are not necessary. A typical advantage associated with providing power over a network is that a user can physically connect a device to the network to transfer information, and the device can be powered without the need of running additional power lines to the physical location of the user. A well known example of a communication network is based on an Ethernet protocol, where information is exchanged between various senders and receivers connected to the network, often through a switch. Power over Ethernet (POE) may be provided through power sourcing equipment (PSE) that distributes power to powered devices (PDs) in a network environment. The network environment for realization of a POE system typically supports the IEEE 802.3af standard.
The type of POE equipment that meets the IEEE 802.3af standard has a number of associated costs, one of the major costs being power supply capacity. The power supply rating is selected to sustain power to certain devices, such as high priority devices, in the event of a power supply failure. The POE equipment can identify and control which devices connected to the network should be powered down in the event of a main power supply failure, so that the remaining devices can be appropriately powered with a backup power supply. Techniques for identifying devices to be powered down, causing the devices to be powered down and assessing the power requirements for devices on the network presently exist where the settings for each of the devices are maintained manually. That is, a designer or user manually causes a particular device to be identified to the POE equipment with appropriate indications for how the device should be controlled in the event of a main power supply failure. For example, the device may be shut down, may proceed through a power on reset (POR) or may continue to be powered with little variation in the input power supply. These types of techniques are somewhat inflexible in that any changes to the device configurations may impact a number of devices and often demand the attention of a skilled professional.
A network with equipment that enables power delivery and distribution over the network can support many different types of equipment, especially equipment connected to a network switch for the transmission of information and power. For example, internet protocol (IP) telephones, wireless access points, IP security cameras, point-of-sale (POS) registers, and so forth, may be connected to a network and receive power while communicating with network equipment. A network manager or designer typically assesses the deployment of different types of equipment and the power needs of the equipment with respect to handling power supply switchovers or failures. Some types of equipment may have high priority for maintaining power such as critical systems in the network, while other equipment may have low priority for maintaining power.
As an example, office environments typically place higher priorities on maintaining the operations of telephones over wireless access points. As another example, a network manager may place a higher priority on POS registers in a retail setting over other less critical equipment. Network switches that supply power to network devices typically have a power supply system with a certain capacitance. In the event of a main power supply failure, that capacitance is drawn upon until the loading of the switch can be reduced, such that a backup supply can accommodate the power needs of the switch, without overload. The backup power supply typically has less power and less capacitance than the main power supply.
One method for supplying power over a network involves the introduction of a power supply at a network connection to inject power into the network. Alternately, network switches that handle information transfer among the network connections may include PSE to deliver power over the network. In either case, typical network power supplies are specified to supply adequate power for expected device loads, while avoiding excess or unused capacity to avoid higher equipment costs. In addition, backup power supplies are often used to supply power to network devices, either in conjunction with a main power supply or as an alternative to the main power supply in the case of a main power supply malfunction. Again to avoid excess costs, backup power supplies are often specified to have a lower rating or capacity than the main power supply.
Network power system designs tend to handle main power supply failures by shutting down non-critical network PDs to match the power load to the capacity of the backup power supply. Main power supplies often have large power storage capacity that can be made available to the network while powered devices on the network are shut down to reduce the load on the network power supply. When the main power supply fails, the power storage maintains power to the network while devices are shut down to reduce the power demand on the backup power supply. The reduction in power demand prevents the lower capacity backup power supply from being overloaded.
The power storage in the main power supply is typically realized as a large capacitance formed with one or more large capacitors. The large capacitance used to provide power to the network during the switchover or power down interval is usually very expensive, and represents a large portion of the overall cost associated with supplying distributed power over the network. However, the large capacitance can be a critical element in maintaining power to devices on the network in the event of a main power supply failure. For example, there may be devices on the network that are considered critical for the network application. Power to these critical devices should not be interrupted, even in the event of a main power supply failure. However, if the typically lower capacity backup power supply is overloaded when the main power supply fails, critical devices may lose power. The large capacitance acts as a power buffer to support a high power demand while non-critical devices are shut down to bring the power demand within the capacity of the backup power supply.
The determination of critical and non-critical devices, that is, device priority, is usually configured at the network power supply control, which is usually found in a network switch, for example. The control is set to power down certain non-critical or low priority devices in the event of a main power supply failure, while maintaining power to critical or high priority devices. The network switch settings take into account the power load of the critical devices so that the backup supply is adequate to the task of maintaining critical device power. Typically, as many devices as possible are powered in the event of a main power supply failure, without overloading the backup power supply. Accordingly, the ports to which network devices are connected are defined in the network switch to either receive power or not in the event of a main power supply failure. Lower priority devices are shut down as rapidly as feasible in the event of a main power supply failure to reduce the latency related to the large capacitance and to avoid overloading the backup power supply.
The faster the lower priority devices can be shut down, the faster a power demand or load that can be handled by the backup power supply is reached. The length of this interval during fast power down determines the rating or size of the large capacitance that supports power supplied to the network during the load change interval. By obtaining a rapid response, the amount of capacitance needed to supply storage power can be reduced, and thereby contribute to reducing overall cost of the power equipment used to power the network device.
When devices connected to the network are set up to receive power, they are given a priority indication for behavior during a main power supply failure event. The network switch is configured to maintain the indication for each PD to cause the low priority devices to be quickly shut down in the event of a main power supply failure. The network switch configuration can be somewhat cumbersome in that each device is manually set to have a particular priority or behavior in the event of a main power supply failure. Anytime a network PD is added to the network, the network switch is manually reconfigured to indicate the behavior of the added device after a main power supply failure. If an added network PD has a higher priority than existing devices that are to be maintained in a powered state, the network designer or manager usually reviews the power budget available from the backup power supply to determine if there is enough backup capacity to power all devices that should be powered after a main power supply failure. If the power consumed by the devices to be powered exceeds the power budget available from the backup power supply, one or more devices are reclassified to be powered down after a main power supply failure. Otherwise, the addition of the high priority device may overload the backup power supply when the main power supply fails, causing the backup supply to shut down or fail. Reclassification of the various devices is therefore important, but can be cumbersome when done manually.
A number of other approaches are available to classify PDs for behavior after a main power supply failure. The various methods offer advantages or disadvantages that are typically related to the network application. Presently, there is no simple way to select or program a given classification method for describing PD behavior in the event of a main power supply failure.